1. Field of the Invention
The invention relates to the arrangement of adjustable resonators between the concoction of a resonator with a bottom, walls and a lid consisting of the transmission path inner conductor casing, which is divided by conductive intermediate walls into resonator cavities. The inner conductor of the resonator cavities is in electrical connection with the inner conductor casing and the resonator cavities in the transmission path of successive cavities are joined by at least one connecting aperture in the separating intermediate walls, the connecting aperture is arranged to form an inductive coupling between the resonator cavities. In addition, the invention relates to a method for forming an adjustable coupling between the resonator cavities.
2. Description of the Prior Art
Common radio frequency resonators are different irons cavity and coaxial resonators, since they can be built with low loss and relatively high powers are sustained by filters containing them. The basic structure of the resonator includes an inner conductor, which includes side walls, an outer conductor, a bottom and a lid. The bottom or base and lid are in a galvanic connection with the outer conductor, and all three together form a closed resonant resonator case. Typically, the lower end of the inner conductor is galvanically linked to the bottom and the upper end to air. When forming a transmission line resonator the inner conductor is short-circuited at its lower end and open at its upper end.
Cavity resonators are commonly used for making the filters in telecommunications networks, in particular, when the transmitted signal power is relatively high. This is because losses are due to smaller resonator filters, which is only a very small attenuation related to the efficiency of the signal. In addition, the response characteristics are well controllable and adjustable to most stringent specifications. Most of the filters and the filter pass band width of the space are intended to be fixed. For some of the filters, the filter passband width is constant. This filter is required in addition to the basic tuning range for the pass-band transmission.
A bandpass filter frequency response arranged to conform to the pass band has to be correctly positioned and must be of the correct band width. In the resonator filter, this requires that the resonant frequency of each resonator is the eigenfrequency of the resonator, and in addition, the couplings between the resonators, have the correct intensity. The series of cavity resonators that constitute the filter are formed with mechanical dimensions so that these conditions are met as well. In practice, the manufacturing process is not accurate enough, so that the filter is tuned before use.
Sequential coupling between the resonators is achieved by the resonator cavity's gap between partition walls, which forms the inductive coupling between the resonators. When the resonators of a device, such as a filter, have the fundamental frequency changed downwardly, the inductive coupling is reduced linearly with frequency. Changing the frequency bands, in turn changes the properties of the device. FIG. 1 shows how a change in resonance frequency in GHz of the adjustable resonators affects the resonant frequency band width (BW) of the coupling. The amount of coupling is described in the pass band width, and its unit is MHz.
The resonators and/or the coupling between the resonators can be tuned by changing the volume of the resonator and/or the coupling. When tuning resonators, vibration occurs in the connections of the resonators. The adjustment of the coupling affects the filter band width. Both of these adjustments (i.e. changing the volume of the resonator cavities and the coupling) can be carried out in several ways. The traditional method is to provide a structure with metallic tuning screws so that the tuning screws extend into the resonator cavities and/or to the coupling between the resonator cavities. For example, rotating the coupling adjustment screw further into the aperture between the resonators to increase the coupling between the resonators, which has a bandwidth broadening effect. Such an excitation is time-consuming and therefore relatively expensive. What is needed is an improved coupling arrangement between cavity filter resonators.